1. Field of the Invention
The present invention relates to a conveyor apparatus for a semiconductor wafer and, more particularly, to a conveyor arm apparatus for a semiconductor wafer, for unloading a semiconductor wafer from a holding chamber and conveying it and for conveying a processed semiconductor wafer and storing it in the holding chamber.
2. Related Background Art
Semiconductor wafers (to be referred to simply as "wafers" hereinafter) used for manufacturing semiconductor elements are often stored in a holding chamber (a so-called a wafer carrier) and are conveyed and processed step by step. For example, in a photolithography process, a plurality of wafers which are stored in the wafer carrier and conveyed to a predetermined position of an exposure apparatus are unloaded from the wafer carrier one by one, and are conveyed on the optical axis of the exposure apparatus. In this case, a method is known wherein wafers are unloaded from the wafer carrier using a plate-like arm (a so-called conveyor arm). With this method, a desired wafer in the wafer carrier can be loaded or unloaded. Therefore, this method is very convenient for the manufacturing process of a semiconductor element in which wafers must be frequently exchanged.
The conveyor arm is inserted between one wafer and a vertically adjacent wafer which are stored in a plurality of racks (or grooves) formed in the two side walls of the wafer carrier. In this case, since the distance between wafers is narrow (normally, about 3 mm to 9 mm), the conveyor arm may contact wafers. Therefore, in order to insert the arm without contacting wafers, a rack distance of the wafer carrier, the thickness of a wafer itself, and the insertion position of the arm must be precisely determined. If wafers are not properly placed on the racks (or grooves) of the wafer carrier, of if the insertion position of the conveyor arm has drifted or the arm is bent, the conveyor arm contacts the upper or lower surface of a wafer during insertion, and this causes generation of dust. In the worst case, the wafer may be damaged.